Any person employed by the Department of Corrections who is a member of the Teachers' Retirement System established under Article 16 of this Code may elect to become a member of this System on either June 1, 1987 or July 1, 1987, by notifying the board of his election in writing on or before May 31, 1987.
For such persons electing to become covered employees, participation in the Article 16 system shall terminate on June 1, 1987, and membership in this System shall begin on that date.
For such persons electing to become noncovered employees, participation in the Article 16 system shall terminate on July 1, 1987, and membership in this System shall begin on that date.
40 ILCS 5/14-108.2